This invention relates generally to numerically controlled machine tools and, more specifically, to a numerically controlled machine tool which is specifically adapted to rapidly machine the interior surface of an elongate tubular workpiece.
Performing machining operations such as drilling milling or profiling on the interior surfaces of an elongate tubular workpiece, such as a torpedo casing, incurs certain difficulties not otherwise incurred in machining the interior surfaces of short tubular workpieces. For example, conventional numerically controlled machine tools, such as horizontal and vertical spindle machining centers and vertical turret lathes, although well suited for machining the interior surfaces of short tubular workpieces, usually are incapable of machining the interior surfaces of elongate tubular workpieces because such machine tools have a limited tool reach. In certain instances where the length of the elongate tubular workpiece, whose interior surfaces are to be machined, is less than twice the tool reach of such machine tools, it may be possible to machine the entire interior surface of the workpiece on such conventional machine tools by repositioning the workpiece after one-half of the interior workpiece surface is machined. However, repositioning the workpiece greatly increases the chances of positioning errors.
To overcome these difficulties, special machines have been constructed to facilitate interior machining of elongate tubular workpieces. An example of such a special machine is the giant stub boring machine described in the November 1974 issue of Tooling and Production which comprises a bed on which a table is slidably mounted for movement thereon along a first axis. Fastened to the table is a tubular workpiece, typically a steam turbine casting, whose central axis is perpendicular to the axis of table movement. A machine tool spindlehead is slidably mounted on the bed for movement thereon along a path perpendicular to the path of table movement and carries an elongate spindle which extends therefrom into the workpiece bore, the spindle being movable on the spindlehead along an axis perpendicular to the axes of table and spindlehead movement. A numerical control system simultaneously regulates spindle speed, table movement, spindle movement and spindlehead movement to effectuate interior machining of the workpiece.
While the above-described stub boring machine is well suited for interior machining of elongate tubular workpieces, it is subject to the disadvantage that the workpiece does not rotate relative to the machine table and thus, to complete a machining operation about the interior circumference of the workpiece bore, the spindle and table are moved under command of the machine tool control system to effectively rotate the spindle about the circumference of the interior workpiece bore. Unfortunately, since the metal chips cut during machining operations tend to accumulate at the bottom-most portion of the workpiece bore, the cutting tool at the end of the spindle will, when machining the bottom-most portion of the workpiece interior, be re-cutting these chips as it engages the interior workpiece surface thereby decreasing machine efficiency.
In contrast, the present invention concerns a machine center, especially adapted for interior machining of elongate tubular workpieces, which includes apparatus for rotating the tubular workpiece relative to the cutting tool so that the cutting tool never engages the bottom-most portion of the workpiece interior, thus avoiding re-cutting of the chips disseminated during prior machining operations.
It is an object of the present invention to provide a machining center especially adapted for machining the interior of elongate tubular workpieces.
It is another object of the present invention to provide a machining center, especially adapted to machine the interior elongate tubular workpieces, which rotates the workpiece relative to the cutting tool so that the cutting tool never engages the bottom-most part of the workpiece, thus avoiding re-cutting of chips disseminated during previous machining operations.